U.S. patent application number 17/309417 was filed with the patent office on 2022-02-10 for aerosol generating apparatus and method of operating same.
The applicant listed for this patent is Nicoventures Trading Limited. Invention is credited to Martin Daniel HORROD, Julian Darryn WHITE.
Application Number | 20220039472 17/309417 |
Document ID | / |
Family ID | 1000005961089 |
Filed Date | 2022-02-10 |
United States Patent
Application |
20220039472 |
Kind Code |
A1 |
WHITE; Julian Darryn ; et
al. |
February 10, 2022 |
AEROSOL GENERATING APPARATUS AND METHOD OF OPERATING SAME
Abstract
An aerosol generating apparatus has a composite susceptor for
heating an aerosol generating material in use thereby to generate
an aerosol. The composite susceptor comprises a support portion and
a susceptor portion supported by the support portion. The apparatus
comprises an induction element arranged for inductive energy
transfer to the susceptor portion in use; and a driving arrangement
arranged to drive the induction element with an alternating current
in use thereby to cause the inductive energy transfer to the
susceptor portion, thereby to cause the heating of the aerosol
generating material by the composite susceptor, thereby to generate
the aerosol. The alternating current has a waveform comprising a
fundamental frequency component having a first frequency and one or
more further frequency components each having a frequency higher
than the first frequency. A method of operating the aerosol
generating apparatus is also disclosed.
Inventors: |
WHITE; Julian Darryn;
(Cambridgeshire, GB) ; HORROD; Martin Daniel;
(Cambridgeshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nicoventures Trading Limited |
London |
|
GB |
|
|
Family ID: |
1000005961089 |
Appl. No.: |
17/309417 |
Filed: |
December 11, 2019 |
PCT Filed: |
December 11, 2019 |
PCT NO: |
PCT/EP2019/084600 |
371 Date: |
May 26, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A24B 15/14 20130101;
H05B 6/108 20130101; H05B 6/06 20130101; A24F 40/465 20200101 |
International
Class: |
A24F 40/465 20060101
A24F040/465; A24B 15/14 20060101 A24B015/14; H05B 6/10 20060101
H05B006/10; H05B 6/06 20060101 H05B006/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2018 |
GB |
1820143.4 |
Claims
1. An aerosol generating apparatus comprising: a composite
susceptor for heating an aerosol generating material in use thereby
to generate an aerosol in use, wherein the composite susceptor
comprises a support portion and a susceptor portion supported by
the support portion; an induction element arranged for inductive
energy transfer to the susceptor portion in use; and a driving
arrangement configured to drive the induction element with an
alternating current in use thereby to cause the inductive energy
transfer to the susceptor portion in use, thereby to cause the
heating of the aerosol generating material by the composite
susceptor in use, thereby to generate the aerosol in use; wherein
the alternating current has a waveform comprising a fundamental
frequency component having a first frequency and one or more
further frequency components each having a frequency higher than
the first frequency.
2. The aerosol generating apparatus according to claim 1, wherein
the susceptor portion is a coating on the support portion.
3. The aerosol generating apparatus according to claim 1, wherein
the susceptor portion comprises a first sheet of a first material
and the support portion comprises a second sheet of a second
material configured to abut the susceptor portion to support the
susceptor portion, wherein the first material and the second
material may be the same or different from one another.
4. The aerosol generating apparatus according to claim 3, wherein
the support portion is configured to surround the susceptor
portion.
5. The aerosol generating apparatus according to a claim 1, wherein
the susceptor portion has a thickness of no more than 50
microns.
6. The aerosol generating apparatus according to claim 1, wherein
the susceptor has a thickness of no more than 20 microns.
7. The aerosol generating apparatus according to claim 1, wherein
the susceptor portion comprises a ferromagnetic material.
8. The aerosol generating apparatus according to claim 1, wherein
the susceptor portion comprises one or more of nickel, aluminum,
and cobalt.
9. (canceled)
10. The aerosol generating apparatus according to claim 1, wherein
the one or more further frequency components are harmonics of the
fundamental component.
11. The aerosol generating apparatus according to claim 1, wherein
the first frequency is a frequency F in the range 0.5 MHz to 2.5
MHz, and the frequency of each of the one or more further frequency
components is nF, where n is a positive integer greater than 1.
12. The aerosol generating apparatus according to claim 1, wherein
the waveform is one of a triangular waveform, a sawtooth waveform,
and a square waveform.
13. The aerosol generating apparatus according to claim 1, wherein
the waveform is a bi-polar square waveform and wherein the driving
arrangement comprises transistors arranged in a H-bridge
configuration and controllable to provide the bi-polar square
waveform.
14. (canceled)
15. The aerosol generating apparatus according to claim 3, wherein
the second material is one or more materials selected from the
group consisting of a metal, a metal alloy, a ceramic material, a
plastic material, and paper.
16. The aerosol generating apparatus according to claim 1, wherein
the composite susceptor comprises a heat resistant protective
portion, wherein the susceptor portion is located between the
support portion and the protective portion.
17. The aerosol generating apparatus according to claim 16, wherein
the heat resistant protective portion is a coating on the susceptor
portion.
18. The aerosol generating apparatus according to claim 16, wherein
the heat resistant protective portion is made of one or more
materials selected from the group consisting of a ceramic material,
a metal nitride, a titanium nitride, and diamond.
19. The aerosol generating apparatus according to claim 1, wherein
the composite susceptor is substantially planar.
20. The aerosol generating apparatus according to claim 1, wherein
the composite susceptor is substantially tubular.
21. The aerosol generating apparatus according to claim 1, wherein
the apparatus comprises the aerosol generating material, wherein
the aerosol generating material is arranged in thermal contact with
the composite susceptor.
22. The aerosol generating apparatus according to claim 21, wherein
the aerosol generating material comprises tobacco and/or one or
more humectants.
23. A method of operating an aerosol generating apparatus, the
aerosol generating apparatus comprising a composite susceptor
arranged for heating an aerosol generating material thereby to
generate an aerosol, the composite susceptor comprising a support
portion and a susceptor portion supported by the support portion;
the apparatus further comprising an induction element arranged for
inductive energy transfer to the susceptor portion; the method
comprising: driving the induction element with an alternating
current thereby to cause the inductive energy transfer to the
susceptor portion, thereby to cause the heating of the aerosol
generating material by the composite susceptor, thereby to generate
the aerosol; wherein the alternating current has a waveform
comprising a fundamental frequency component having a first
frequency and one or more further frequency components each having
a frequency higher than the first frequency.
24. The method according to claim 23, wherein the one or more
further frequency components are harmonics of the fundamental
frequency component.
25. The method according to claim 23, wherein the first frequency
is a frequency F in the range 0.5 MHz to 2.5 MHz, and the frequency
of each of the one or more further frequency components is nF,
where n is a positive integer greater than 1.
26. The method according to claim 23, wherein the waveform is one
of a triangular waveform, a sawtooth waveform, a bi-polar square
waveform, and a square waveform.
27. (canceled)
28. (canceled)
Description
PRIORITY CLAIM
[0001] The present application is a National Phase entry of PCT
Application No. PCT/EP2019/084600, filed Dec. 11, 2019, which
claims priority from Great Britain Application No. 1820143.4, filed
Dec. 11, 2018, each of which is hereby fully incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates an aerosol generating
apparatus and a method of operating same.
BACKGROUND
[0003] Smoking articles such as cigarettes, cigars and the like
burn tobacco during use to create tobacco smoke. Attempts have been
made to provide alternatives to these articles by creating products
that release compounds without combusting. Examples of such
products are so-called "heat not burn" products or tobacco heating
devices or products, which release compounds by heating, but not
burning, material. The material may be, for example, tobacco or
other non-tobacco products, which may or may not contain
nicotine.
SUMMARY
[0004] According to a first aspect of the present invention, there
is provided an aerosol generating apparatus comprising: a composite
susceptor for heating an aerosol generating material in use thereby
to generate an aerosol in use, wherein the composite susceptor
comprises a support portion and a susceptor portion supported by
the support portion; an induction element arranged for inductive
energy transfer to the susceptor portion in use; and a driving
arrangement arranged to drive the induction element with an
alternating current in use thereby to cause the inductive energy
transfer to the susceptor portion in use, thereby to cause the
heating of the aerosol generating material by the composite
susceptor in use, thereby to generate the aerosol in use; wherein
the alternating current has a waveform comprising a fundamental
frequency component having a first frequency and one or more
further frequency components each having a frequency higher than
the first frequency.
[0005] Optionally, the susceptor portion is formed as a coating on
the support portion.
[0006] Optionally, the susceptor portion comprises a first sheet of
material and the support portion comprises a second sheet of
material configured to abut the susceptor portion to support the
susceptor portion.
[0007] Optionally, the support portion is configured to surround
the susceptor portion.
[0008] Optionally, the susceptor portion has a thickness of
substantially no more than 50 microns.
[0009] Optionally the susceptor has a thickness of substantially no
more than 20 microns.
[0010] Optionally, the susceptor portion comprises a ferromagnetic
material.
[0011] Optionally, the susceptor portion comprises one or more of
nickel and cobalt.
[0012] Optionally, the one or more further components are harmonics
of the fundamental component.
[0013] Optionally, the first frequency is a frequency F in the
range 0.5 MHz to 2.5 MHz, and the frequency of each of the one or
more further frequency components is nF, where n is a positive
integer greater than 1.
[0014] Optionally, the waveform is one of a substantially
triangular waveform, a substantially sawtooth waveform, and a
substantially square waveform.
[0015] Optionally, the waveform is a bi-polar square waveform.
[0016] Optionally, the driving arrangement comprises transistors
arranged in a H-bridge configuration and controllable to provide
the bi-polar square waveform.
[0017] Optionally, the support portion comprises one or more of a
metal, a metal alloy, a ceramics material, a plastics material, and
paper.
[0018] Optionally, the composite susceptor comprises a heat
resistant protective portion, wherein the susceptor portion is
located between the support portion and the protective portion.
[0019] Optionally, the heat resistant protective portion is a
coating on the susceptor portion.
[0020] Optionally, the heat resistant protective portion comprises
one or more of a ceramics material, metal nitride, titanium
nitride, and diamond.
[0021] Optionally, the composite susceptor is substantially
planar.
[0022] Optionally, the composite susceptor is substantially
tubular.
[0023] Optionally, the apparatus comprises the aerosol generating
material, wherein the aerosol generating material is in thermal
contact with the composite susceptor.
[0024] Optionally, the aerosol generating material comprises
tobacco and/or one or more humectants.
[0025] According to a second aspect of the present invention, there
is provided a method of operating an aerosol generating apparatus,
the aerosol generating apparatus comprising a composite susceptor
arranged for heating an aerosol generating material thereby to
generate an aerosol, the composite susceptor comprising a support
portion and a susceptor portion supported by the support portion;
the apparatus further comprising an induction element arranged for
inductive energy transfer to the susceptor portion; the method
comprising: driving the induction element with an alternating
current thereby to cause the inductive energy transfer to the
susceptor portion, thereby to cause the heating of the aerosol
generating material by the composite susceptor, thereby to generate
the aerosol; wherein the alternating current has a waveform
comprising a fundamental frequency component having a first
frequency and one or more further frequency components each having
a frequency higher than the first frequency.
[0026] Optionally, the one or more further frequency components are
harmonics of the fundamental frequency component.
[0027] Optionally, the first frequency is a frequency F in the
range 0.5 MHz to 2.5 MHz, and the frequency of each of the one or
more further frequency components is nF, where n is a positive
integer greater than 1.
[0028] Optionally, the waveform is one of a triangular waveform, a
sawtooth waveform, and a square waveform.
[0029] Optionally, the waveform is a bi-polar square waveform.
[0030] Optionally, the aerosol generating apparatus is the aerosol
generating apparatus according to the first aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Further features and advantages will now be described, by
way of example only, with reference to the accompanying drawings of
which:
[0032] FIG. 1 illustrates schematically an aerosol generating
apparatus according to an example;
[0033] FIG. 2 illustrates schematically a composite susceptor
according to a first example;
[0034] FIG. 3 illustrates schematically a composite susceptor
according to a second example;
[0035] FIG. 4 illustrates schematically a portion of the aerosol
generating apparatus of FIG. 1;
[0036] FIG. 5 illustrates schematically a portion of a driving
arrangement according to an example;
[0037] FIGS. 6a, 6c, 6e, 6g, and 6i each illustrate schematically a
plot of current against time for different alternating current
waveforms;
[0038] FIGS. 6b, 6d, 6f, 6h, and 6j each illustrate schematically a
plot in frequency space of the frequency components of the
alternating current waveforms of FIGS. 6a, 6c, 6e, 6g, and 6i,
respectively; and
[0039] FIG. 7 illustrates schematically a method of operating an
aerosol generating device, according to an example.
DETAILED DESCRIPTION OF THE DRAWINGS
[0040] Induction heating is a process of heating an electrically
conducting object (or susceptor) by electromagnetic induction. An
induction heater may comprise an induction element, such as an
electromagnet, and circuitry for passing a varying electric
current, such as an alternating electric current, through the
electromagnet. The varying electric current in the electromagnet
produces a varying magnetic field. The varying magnetic field
penetrates a susceptor suitably positioned with respect to the
electromagnet, generating eddy currents inside the susceptor. The
susceptor has electrical resistance to the eddy currents, and hence
the flow of the eddy currents against this resistance causes the
susceptor to be heated by Joule heating. In cases where the
susceptor comprises ferromagnetic material such as iron, nickel or
cobalt, heat may also be generated by magnetic hysteresis losses in
the susceptor, i.e. by the varying orientation of magnetic dipoles
in the magnetic material as a result of their alignment with the
varying magnetic field.
[0041] In inductive heating, as compared to heating by conduction
for example, heat is generated inside the susceptor, allowing for
rapid heating. Further, there need not be any physical contact
between the inductive heater and the susceptor, allowing for
enhanced freedom in construction and application.
[0042] An induction heater may comprise an RLC circuit, comprising
a resistance (R) provided by a resistor, an inductance (L) provided
by an induction element, for example the electromagnet which may be
arranged to inductively heat a susceptor, and a capacitance (C)
provided by a capacitor, for example connected in series or in
parallel. In some cases, resistance is provided by the ohmic
resistance of parts of the circuit connecting the inductor and the
capacitor, and hence the RLC circuit need not necessarily include a
resistor as such. Such a circuit may be referred to, for example as
an LC circuit. Such circuits may exhibit electrical resonance,
which occurs at a particular resonant frequency when the imaginary
parts of impedances or admittances of circuit elements cancel each
other. Resonance occurs in an RLC or LC circuit because the
collapsing magnetic field of the inductor generates an electric
current in its windings that charges the capacitor, while the
discharging capacitor provides an electric current that builds the
magnetic field in the inductor. When the circuit is driven at the
resonant frequency, the series impedance of the inductor and the
capacitor is at a minimum, and circuit current is maximum. Driving
the RLC or LC circuit at or near the resonant frequency may
therefore provide for effective and/or efficient inductive
heating.
[0043] FIG. 1 illustrates schematically an aerosol generating
apparatus 100, according to an example. The apparatus 100 is an
aerosol generating device 100. The aerosol generating device 100 is
hand held. The aerosol generating device 100 comprises a DC power
source 104, in this example a battery 104, a driving arrangement
106, an induction element 108, a composite susceptor 110, and
aerosol generating material 116.
[0044] In broad overview, the composite susceptor 110 (which
comprises a support portion and a susceptor portion supported by
the support portion, described in more detail below) is for heating
the aerosol generating material in use to generate an aerosol in
use, the induction element 108 is arranged for inductive energy
transfer to at least the susceptor portion of the composite
susceptor 110 in use, and the driving arrangement 106 is arranged
to drive the induction element 108 with an alternating current in
use thereby to cause the inductive energy transfer to the susceptor
portion of the composite susceptor 110 in use, thereby to cause the
heating of the aerosol generating material 116 by the composite
susceptor 110 in use, thereby to generate the aerosol in use. The
alternating current has a waveform comprising a fundamental
frequency component having a first frequency and one or more
further frequency components each having a frequency higher than
the first frequency. For example, the waveform may be a
substantially square waveform.
[0045] In broad overview, driving the induction element with a
current having a waveform comprising a fundamental frequency
component and one or more further frequency components of higher
frequency, in turn causes the alternating magnetic field produced
by the induction element to comprise a fundamental frequency
component and one or more further frequency components of higher
frequency. The skin depth (i.e. the characteristic depth into which
the alternating magnetic field produced by the induction element
108 penetrates into the susceptor portion to cause inductive
heating) decreases with increasing frequency of the alternating
magnetic field. Therefore, the skin depth for the higher frequency
components is less than the skin depth for the fundamental
frequency component. Using a waveform comprising the fundamental
frequency component and the one or more higher frequency components
may therefore allow a greater proportion of the inductive energy
transfer from the induction element to the susceptor to occur in
relatively small depth from the surface of the susceptor, for
example as compared to using the fundamental frequency alone. This
may allow the thickness of susceptor portion to be reduced while
still substantially maintaining a given energy transfer efficiency,
which may in turn allow the cost of the susceptor portion to be
reduced (and/or the efficiency of producing the susceptor portion
to be increased). Alternatively or additionally, this may allow the
energy transfer efficiency to be increased for a given susceptor
portion thickness (for example one in which the skin depth might
otherwise be larger than the thickness of the susceptor portion),
which may in turn allow an improved heating efficiency. An improved
aerosol generating device and method for producing an aerosol may
therefore be provided.
[0046] Returning to FIG. 1, the DC power source 104 is electrically
connected to the driving arrangement 106. The DC power source is
104 is arranged to provide DC electrical power to the driving
arrangement 106. The driving arrangement 106 is electrically
connected to the induction element 108. The driving arrangement 106
is arranged to convert an input DC current from the DC power source
104 into an alternating current. The driving arrangement 106 is
arranged to drive the induction element 108 with the alternating
current. In other words, the driving arrangement 106 is arranged to
drive the alternating current through the induction element 108,
that is to cause an alternating current to flow through the
induction element 106.
[0047] The induction element 108 may be, for example, an
electromagnet, for example a coil or solenoid, which may for
example be planar, which may for example be formed from copper. The
induction element 108 is arranged for inductive energy transfer to
the composite susceptor 110 in use (i.e. to at least the susceptor
portion of the composite susceptor 110, as described in more detail
below). Equally, the composite susceptor 110 is arranged relative
to the induction element 108 for inductive energy transfer from the
induction element 108 to the composite susceptor 110.
[0048] The induction element 108, having alternating current driven
therethrough, causes the composite susceptor 110 to heat up by
Joule heating and/or by magnetic hysteresis heating, as described
above. For example, the composite susceptor 110 is in thermal
contact with the aerosol generating material 116 (i.e. arranged to
heat the aerosol generating material 116 for example by conduction,
convection, and/or radiation heating, to generate an aerosol in
use). In some examples, the composite susceptor 110 and the aerosol
generating material 116 form an integral unit that may be inserted
and/or removed from the aerosol generating device 100 and may be
disposable. In some examples, the induction element 108 may be
removable from the device 100, for example for replacement. The
aerosol generating device 100 may be arranged to heat the aerosol
generating material 116 to generate aerosol for inhalation by a
user.
[0049] It is noted that, as used herein, the term "aerosol
generating material" includes materials that provide volatilized
components upon heating, typically in the form of vapor or an
aerosol. Aerosol generating material may be a
non-tobacco-containing material or a tobacco-containing material.
For example, the aerosol generating material may be or comprise
tobacco. Aerosol generating material may, for example, include one
or more of tobacco per se, tobacco derivatives, expanded tobacco,
reconstituted tobacco, tobacco extract, homogenized tobacco or
tobacco substitutes. The aerosol generating material can be in the
form of ground tobacco, cut rag tobacco, extruded tobacco,
reconstituted tobacco, reconstituted material, liquid, gel, gelled
sheet, powder, or agglomerates, or the like. Aerosol generating
material also may include other, non-tobacco, products, which,
depending on the product, may or may not contain nicotine. Aerosol
generating material may comprise one or more humectants, such as
glycerol and/or propylene glycol.
[0050] Returning to FIG. 1, the aerosol generating device 100
comprises an outer body 112 housing the battery 104, the driving
arrangement 106, the induction element 108, the composite susceptor
110, and the aerosol generating material 116. The outer body 112
comprises a mouthpiece 114 to allow aerosol generated in use to
exit the device 100. In some implementations, however, the aerosol
generating material 116 and the mouthpiece 114 may be provided in a
combined structure which is inserted into the device 100 (e.g., a
paper-wrapped tube of tobacco or tobacco containing material
comprising a filter material at one end).
[0051] In use, a user may activate, for example via a button (not
shown) or a puff detector (not shown) which is known per se, the
circuitry 106 to cause alternating current to be driven through the
induction element 108, thereby inductively heating the composite
susceptor 116, which may in turn heat the aerosol generating
material 116, and cause the aerosol generating material 116 thereby
to generate an aerosol. The aerosol is generated into air drawn
into the device 100 from an air inlet (not shown), and is thereby
carried to the mouthpiece 114, where the aerosol exits the device
100.
[0052] The driver arrangement 106, induction element 108, composite
susceptor 110 and/or the device 100 as a whole may be arranged to
heat the aerosol generating material 116 to a range of temperatures
to volatilize at least one component of the aerosol generating
material without combusting the aerosol generating material 116.
For example, the temperature range may be about 50.degree. C. to
about 350.degree. C., such as between about 100.degree. C. and
about 250.degree. C., between about 150.degree. C. and about
230.degree. C. In some examples, the temperature range is between
about 170.degree. C. and about 220.degree. C. In some examples, the
temperature range may be other than this range, and the upper limit
of the temperature range may be greater than 300.degree. C.
[0053] Referring now to FIG. 2, there is illustrated an example
composite susceptor 210. The example composite susceptor 210 may be
used as the composite susceptor 110 in the aerosol generating
device 100 described with reference to FIG. 1. The composite
susceptor 210 may be substantially planar (as illustrated in FIG.
2). In other examples, the composite susceptor 210 may be
substantially tubular. For example, the composite susceptor 210 may
surround the aerosol generating material (not shown in FIG. 2),
i.e. the aerosol generating material may be placed inside the
tubular composite susceptor 210. As another example, the aerosol
generating material may be arranged around the tubular composite
susceptor 210 so as to surround the tubular composite susceptor
210. The composite susceptor 210 being tubular may help improve
heating efficiency of the aerosol generating material.
[0054] The composite susceptor 210 comprises a support portion 222
and a susceptor portion 224. The susceptor portion 224 is supported
by the support portion 222 (that is the support portion 222
supports the susceptor portion 224). The susceptor portion 224 is
capable of inductive energy transfer with the induction element
(e.g. 106 of FIG. 1) such that an alternating magnetic field
produced by the induction element causes the susceptor portion 224
to be inductively heated, for example by Joule heating and/or
magnetic hysteresis heating as described above (i.e. the susceptor
portion 224 acts as a susceptor in use). The susceptor portion 224
may comprise an electrically conductive material, such as metal,
and/or a conductive polymer. The susceptor portion may comprise a
ferromagnetic material, for example one or both of nickel and
cobalt. In some examples, the support portion 222 may also
substantially act as a susceptor. In other examples, the support
portion 222 may substantially not be inductively heatable. The
support portion 222 may comprise one or more of a metal, a metal
alloy, a ceramics material, a plastics material, and paper. For
example, the support portion 222 may be or comprise stainless
steel, aluminum, steel, copper, and/or high temperature (i.e. heat
resistant) polymers such as Polyether ether ketone (PEEK) and/or
Kapton and/or polyamide resins such as Zytel.RTM. HTN.
[0055] The susceptor portion 224 may be formed as a coating on the
support portion 222. For example, the susceptor portion 224 may be
coated with a ferromagnetic material, for example nickel and/or
cobalt. For example, the coating may be formed by chemical plating,
for example electrochemical plating, and/or by vacuum evaporation
of the material of the susceptor portion 224 onto the support
portion 222. In some examples, the thickness of the susceptor
portion 204 may be substantially no more than 50 microns, for
example no more than 20 microns, for example between around 10 to
20 microns, for example around 15 microns or for example a few
microns.
[0056] A composite susceptor 110 comprising a susceptor portion 204
of ferromagnetic material such as nickel or cobalt, (e.g. on a side
of the composite susceptor 110 facing the induction element 108)
may allow for the susceptor portion 204 to be made relatively thin
while effecting a similar inductive energy absorption as a thicker
mild steel plate, for example. Cobalt may be preferred as it has a
higher magnetic permeability and hence may allow for improved
inductive energy absorption. Further, cobalt has a higher Curie
point temperature than nickel (around 1,120 to 1,127 degrees
Celsius for cobalt, versus 353 to 354 degrees Celsius for nickel).
At or towards the curie point temperature, magnetic permeability of
the susceptor material may reduce or cease, and the ability of the
material to be heated by penetration with a varying magnetic field
may also reduce or cease. The curie point temperature of cobalt may
be above the normal operating temperatures of the inductive heating
of the aerosol generating device 100, and hence the effect of the
reduced magnetic permeability may be less pronounced (or
indiscernible) during normal operation if cobalt is used as
compared to if nickel is used. As mentioned above, the support
portion 222 of the composite susceptor 210 need not interact with
the applied varying magnetic field to generate heat for heating the
aerosol generating material 116, rather only to support the
susceptor portion 222. Accordingly, the support can be made from
any suitable heat resistant material. Example materials are
aluminum, steel, copper, and high temperature polymers such as
polyether ether ketone (PEEK), Kapton or paper.
[0057] Using a relatively low thickness of susceptor material, for
example a ferromagnetic material such as nickel or cobalt may allow
relatively little of the susceptor material to be used, which may
allow for a more efficient/reduced cost susceptor production. Using
relatively thin susceptor material alone may produce a susceptor
prone to damage, for example due to the fragility of such materials
at thicknesses in the range of 10s of microns. However, having the
susceptor portion 224 supported by, for example formed as a coating
on or being surrounded by, the support portion 222 may allow for a
low cost susceptor to be produced but which is relatively resistant
to damage. As mentioned above, since the support portion 222 need
not necessarily provide the function of being susceptible to
inductive heating, the support portion 222 may be made from a wider
variety of heat resistant materials, such as a metal, a metal
alloy, a ceramics material, and a plastics material, which may be
of relatively low cost. Therefore, the composite susceptor 210 may
be made with relatively low cost.
[0058] Referring now to FIG. 3, there is illustrated schematically
an example composite susceptor 310. The example composite susceptor
210 may be used as the composite susceptor 110 in the aerosol
generating device 100 described with reference to FIG. 1. The
composite susceptor 310 illustrated in FIG. 3 may be the same as
the example susceptor 210 described above with reference to FIG. 2,
except that the composite susceptor 310 illustrated in FIG. 3
comprises a heat resistant protective portion 326. The composite
susceptor 310 comprises a support portion 322 (which may be the
same or similar to the support portion 222 of the composite
susceptor 210 of FIG. 2), and a susceptor portion 324 (which may be
the same or similar to the susceptor portion 224 of the composite
susceptor 210 of FIG. 2). In this example, the susceptor portion
324 is located between the support portion 322 and the protective
portion 326.
[0059] The heat resistant protective portion 326 may be a coating
on the susceptor portion 324.
[0060] The heat resistant protective portion 326 may comprise one
or more of a ceramics material, metal nitride, titanium nitride,
and diamond-like-carbon. For example, titanium nitride and/or
diamond-like-carbon may be applied as a coating using physical
vapor deposition. The protective portion 326 may protect the
susceptor portion 324 from chemical corrosion, such as surface
oxidation, which may otherwise have a propensity to occur, for
example as a result of the inductive heating of the composite
susceptor, and which may otherwise shorten the lifespan of the
composite susceptor 310. The protective portion 326 may
alternatively or additionally protect the susceptor portion 324
from mechanical wear, which may otherwise shorten the lifespan of
the composite susceptor. The protective portion 326 may
alternatively or additionally reduce the heat loss from the
susceptor portion 324, which may otherwise be lost to the
environment, and hence the protective portion 326 may improve the
heating efficiency of the composite susceptor 310.
[0061] For example, where the susceptor portion 324 is of a
ferromagnetic material such as cobalt or nickel, the susceptor
portion 324 may become increasingly susceptible to oxidation as it
increases in temperature. This may increase heat loss due to
radiation by increasing the relative emissivity (.epsilon.r)
relative to the unoxidized metal surface, enhancing the rate at
which energy is lost through radiation. If the energy radiated ends
up being lost to the environment, then such radiation can reduce
the system energy efficiency. Oxidation may also reduce the
resistance of the susceptor portion 324 to chemical corrosion,
which may result in shortening the service life of the heating
element. The heat resistant protective portion 326 may reduce these
effects. As mentioned above, in some examples, the protective
portion 326 may be applied by physical vapor deposition, but in
other examples the protective portion 326 may be provided by
chemically treating the susceptor portion 324 to encourage growth
of a protective film over the susceptor portion 324, or formation
of a protective oxide layer using a process such as anodization. In
some examples, the susceptor portion may be encapsulated, for
example, the heat resistant protective portion 326 and the support
portion 322 may together encapsulate the susceptor portion 224. In
some examples, the heat resistant protective portion 326 may
encapsulate the susceptor portion 324 and the support portion 322.
In some examples, the heat resistant protective portion 326 may
have low or no electrical conductivity, which may prevent the
induction of electric currents in the heat resistant protective
portion 326 rather than the susceptor portion 324.
[0062] FIG. 4 illustrates schematically in more detail some of the
components of the apparatus 100 described above with reference to
FIG. 1, according to an example. Components that are the same or
similar to those described above with reference to FIG. 1 are given
the same reference numerals and will not be described in detail
again.
[0063] Referring to FIG. 4, the driving arrangement 106 comprises a
driver 432 and a driver controller 430. The driver 432 is
electrically connected to the battery 104. Specifically, the driver
432 is connected to a positive terminal of the battery 104, that
provides relatively high electric potential+v 434, and to a
negative terminal of the battery or to ground, which provides a
relatively low or no or negative electric potential GND 436. A
voltage is therefore established across the driver 432.
[0064] The driver 432 is electrically connected to the induction
element 108. The induction element may have an inductance L. The
driver 432 may be electrically connected to the induction element
108 via a circuit comprising a capacitor (not shown) having a
capacitance C and the induction element 108 connected in series,
i.e. a series LC circuit.
[0065] The driver 432 is arranged to provide, from an input direct
current from the battery 104, an alternating current to the
induction element 108 in use. The driver 432 is electrically
connected to a driver controller 430, for example comprising logic
circuitry. The driver controller 430 is arranged to control the
driver 432, or components thereof, to provide the output
alternating current from the input direct current. In one example,
as described in more detail below, the driver controller 430 may be
arranged to control the provision of a switching potential to
transistors of the driver 432 at varying times to cause the driver
432 to produce the alternating current. The driver controller 430
may be electrically connected to the battery 104, from which the
switching potential may be derived.
[0066] The driver controller 430 may be arranged to control the
frequency of alternating current driven through the induction
element 108. As mentioned above, LC circuits may exhibit resonance.
The driver controller 208 may control the frequency of the
alternating current driven through a series LC circuit comprising
the induction element 108 to be at or near the resonant frequency
of the LC circuit. For example, the drive frequency may be in the
MHz (Mega Hertz) range, for example in the range 0.5 to 2.5 MHz for
example 2 MHz. It will be appreciated that other frequencies may be
used, for example depending on the particular circuit (and/or
components thereof), and/or susceptor 110 used. For example, it
will be appreciated that the resonant frequency of the circuit may
be dependent on the inductance L and capacitance C of the circuit,
which in turn may be dependent on the inductor 108, capacitor (not
shown) and susceptor 110 used. It should be noted that in some
examples, the capacitance may be zero or close to zero. In such
examples, the resonant behavior of the circuit may be
negligible.
[0067] The driving arrangement 106 may be arranged to control the
waveform of the alternating current produced. In one example, as
described in more detail below, the waveform may be a square wave
form, for example a bi-polar square wave form. In other examples,
the waveform may be a triangular waveform or a sawtooth waveform,
or indeed any waveform comprising a fundamental frequency component
having a first frequency and one or more further frequency
components each having a frequency higher than the first frequency.
In this regard, the fundamental frequency of the waveform is the
drive frequency of the LC circuit.
[0068] In use, when the driver controller 430 is activated, for
example by a user, the driver controller 430 may control the driver
432 to drive alternating current through the induction element 108,
thereby inductively heating the susceptor 110 (which then may heat
an aerosol generating material (not shown in FIG. 4) to produce an
aerosol for inhalation by a user, for example).
[0069] Referring now to FIG. 5, there is illustrated schematically
in more detail a driver 432 according to an example. The driver 432
illustrated in FIG. 5 may be used as the driver 432 described above
with reference to FIG. 4, and/or may be used as part of the driving
arrangement 106 described above with reference to FIGS. 1 and/or 4.
In this example, the driver 432 is a H-bridge driver 432. The
driver 432 comprises a plurality of transistors, in this example
four transistors Q1, Q2, Q3, Q4, arranged in a H-bridge
configuration (note that transistors arranged or connected in a
H-bridge configuration may be referred to as a H-bridge). The
H-bridge configuration comprises a high side pair transistors Q1,
Q2 and a low side pair of transistors Q3, Q4. A first transistor Q1
of the high side pair is electrically adjacent to a third
transistor Q3 of the low side pair, and a second transistor Q2 of
the high side pair is electrically adjacent to a fourth transistor
of the low side pair. The high side pair are for connection to a
first electric potential+v 434 higher than a second electric
potential GND 436 to which the low side pair are for connection. In
this example, the driver 432 is arranged for connection of the DC
power source 104 (not shown in FIG. 5) across a first point 545
between the high side pair 304 of transistors Q1, Q2 and a second
point 546 between the low side pair 306 of transistors Q3, Q4. In
use therefore, a potential difference is established between the
first point 545 and the second point 546.
[0070] The example driver 432 illustrated in FIG. 5 is electrically
connected to, and arranged to drive, the induction element 108.
Specifically, the induction element 108 is connected across a third
point 548 between one of the high side pair of transistors Q2 and
one of the low side pair of transistors Q4 and a fourth point 547
between the other of the high side pair of transistors Q1 and the
other of low side second pair of transistors Q3.
[0071] In this example, each transistor is a field effect
transistor Q1, Q2, Q3, Q4 controllable by a switching potential
provided by the driver controller (not shown in FIG. 5), via
control lines 541, 542, 543, 544 respectively, to substantially
allow current to pass therethrough in use. For example, each field
effect transistor Q1, Q2, Q3, Q4 is arranged such that, when the
switching potential is provided to the field effect transistor Q1,
Q2, Q3, Q4 then the field effect transistor Q1, Q2, Q3, Q4,
substantially allows current to pass therethrough, and when the
switching potential is not provided to the field effect transistor
Q1, Q2, Q3, Q4, then the field effect transistor Q1, Q2, Q3, Q4
substantially prevents current from passing therethrough.
[0072] In this example, the driver controller (not shown in FIG. 5,
but see the driver controller 430 in FIG. 4) is arranged to control
supply of the switching potential to each field effect transistor,
via supply lines 541, 542, 543, 544 independently, thereby to
independently control whether each respective transistor Q1, Q2,
Q3, Q4 is in an "on" mode (i.e. low resistance mode where current
passes therethrough) or an "off" mode (i.e. high resistance mode
where substantially no current passes therethrough).
[0073] By controlling the timing of the provision of the switching
potential to the respective field effect transistors Q1, Q2, Q3,
Q4, the driver controller 430 may cause alternating current to be
provided to the induction element 108. For example, at a first
time, the driver controller 430 may be in a first switching state,
where a switching potential is provided to the first and the fourth
field effect transistors Q1, Q4, but not provided to the second and
the third field effect transistors Q2, Q3. Hence the first and
fourth field effect transistors Q1, Q4 will be in a low resistance
mode, whereas second and third field effect transistors Q2, Q3 will
be in a high resistance mode. Therefore, at this first time,
current will flow from the first point 545 of the driver 432,
through the first field effect transistor Q1, through the induction
element 108 in a first direction (left to right in the sense of
FIG. 5), through the fourth field effect transistor Q4 to the
second point 546 of the driver 432. However, at a second time, the
driver controller 430 may be in a second switching state, where a
switching potential is provided to the second and third field
effect transistors Q2, Q3, but not provided to the first and the
fourth field effect transistors Q1, Q4. Hence the second and third
field effect transistors Q2, Q3 will be in a low resistance mode,
whereas first and fourth field effect transistors Q1, Q4 will be in
a high resistance mode. Therefore, at this second time, current
will flow from the first point 545 of the driver 432, through the
second field effect transistor Q2, through the induction element
108 in a second direction opposite to the first direction (i.e.
right to left in the sense of FIG. 5), through the third field
effect transistor Q3 to the second point 546 of the driver 432. By
alternating between the first and second switching state therefore,
the driver controller 430 may control the driver 432 to provide
(i.e. drive) alternating current through the induction element 108.
In such a way, the driver arrangement 106 may therefore drive an
alternating current through the induction element 108.
[0074] In this example, the alternating current driven through the
induction element 108 may have a substantially square waveform.
Specifically, the alternating current will have a substantially
bi-polar square wave form (that is, the waveform of the alternating
current has both a first substantially square portion for positive
current values (i.e. current flowing in a first direction at the
first time), and a second substantially square portion for negative
current values (i.e. current flowing in a second direction opposite
to the first direction at the second time). As described in more
detail below however, in other example, other driving arrangements
106 may be used to produce alternating current having other forms.
For example, the driving arrangement 106 may comprise a signal
generator such as a function generator or an arbitrary waveform
generator capable of generating one or more types of waveforms,
which then may be used, for example with suitable amplifiers, to
cause alternating current to be driven in the induction element 108
in accordance with that waveform.
[0075] Referring now to FIGS. 6a to 6j, FIGS. 6b, 6d, 6f, 6h, and
6j each illustrate schematically a plot in frequency space of the
frequency components of the alternating current waveforms of FIGS.
6a, 6c, 6e, 6g, and 6i, respectively.
[0076] FIG. 6a illustrates schematically a sine waveform of
alternating current I as a function of time t. The sine waveform
has a frequency F, in other words, in FIG. 6a, the current I varies
as a function of time t according to the equation I=sin (2.pi.Ft).
FIG. 6b illustrates schematically a plot in frequency space of the
frequency components of the sine waveform in FIG. 6a. In other
words, the plot in FIG. 6b may be taken as representing the Fourier
transform of the waveform of FIG. 6b. Specifically, FIG. 6b plots
amplitude A of the waveform against frequency! In the schematic
plot of FIG. 6b, the amplitude A has been normalized so as to be 1
for the largest amplitude A of the spectrum. The plot of FIG. 6b
illustrates that the pure sine waveform of FIG. 6a only has one
frequency component at frequency F. In other words, all of the
amplitude or energy of the sine waveform of FIG. 6a is contained at
the frequency F, i.e. the fundamental frequency component of the
waveform.
[0077] FIG. 6c illustrates schematically a plot of another example
waveform of alternating current I as a function of time t. In this
example, the waveform comprises a fundamental sine component having
a frequency F, as well as a further sine component having frequency
2F. In other words, in FIG. 6c, the current I varies as a function
of time t according to the equation I=sin (2.pi.Ft)+Bsin
(2.pi.2Ft), where B is an arbitrary constant. FIG. 6d illustrates
schematically a plot in frequency space (i.e. frequency f against
amplitude A) of the frequency components of the waveform in FIG.
6c. Again, the amplitude A has been normalized so as to be 1 for
the largest amplitude A of the spectrum. The plot of FIG. 6d
illustrates that the waveform of FIG. 6c has a fundamental
frequency component having a frequency F, and a further frequency
component having a frequency of 2F. As illustrated, some of the
amplitude or energy of the waveform of FIG. 6c is contained at the
frequency F, i.e. the fundamental frequency component of the
waveform, and some of the amplitude or energy of the waveform is
contained at the frequency 2F (i.e. at a frequency two times that
of F).
[0078] FIG. 6e illustrates schematically another example plot of a
waveform of alternating current/as a function of time t. In this
example, the waveform is a square waveform, specifically a bi-polar
square waveform (i.e. where the waveform comprises a square portion
of positive current flow followed by a square portion of negative
current flow). In this example, the square waveform has a
fundamental frequency F. As is known, the Fourier expansion of a
square wave comprises a sum (in the ideal an infinite sum, but in
practice not infinite) of sine waves, comprising the fundamental
frequency component at frequency F, and further frequency
components at odd integer k multiples of F, where the relative
amplitudes of the frequency components are given by 1/k. For
example, if the amplitude of the fundamental frequency component of
frequency F is taken as 1, then the amplitude of the first further
frequency component at frequency 3F would be 1/3, the amplitude of
the second frequency component at frequency 5F would be 1/5, the
amplitude of the third frequency component at frequency 7F would be
1/7, and so on. For ease of reference, this series may be
represented according to the convention (F)+1/3(3F)+1/5(5F)+
1/7(7F)+ . . . . FIG. 6f illustrates schematically a plot in
frequency space (i.e. frequency f against amplitude A) of the
frequency components of the waveform in FIG. 6e. Again, the
amplitude A has been normalized so as to be 1 for the largest
amplitude A of the spectrum. The plot of FIG. 6f illustrates that,
the square waveform comprises the fundamental frequency component
having frequency F, as well as further frequency components at odd
integer multiples (odd harmonics) of the fundamental frequency F,
i.e. 3F, 5F, etc., having relative amplitudes represented as 1(F);
1/3(3F); 1/5(5F) etc. In other words, as illustrated, some of the
amplitude or energy of the waveform of FIG. 6e is contained at the
frequency F, i.e. the fundamental frequency component of the
waveform; a third as much energy as in the fundamental frequency
component is contained in the further frequency component at
frequency 3F, and a fifth as much energy as in the fundamental
frequency component is contained in the further frequency component
at frequency 5F (and so on). In general, around 80% of the energy
of the square wave form is contained within the fundamental
frequency component, and around 20% of the energy of the square
waveform is contained in the further frequency components of higher
frequency.
[0079] FIG. 6g illustrates schematically another example plot of a
waveform of alternating current I as a function of time t. In this
example, the waveform is a triangular waveform. In this example,
the triangular waveform has a fundamental frequency F. As is known,
the Fourier expansion of a triangular wave comprises a sum (in the
ideal an infinite sum, but in practice not infinite) of sine waves,
conforming to a sequence (in the form of the above introduced
convention) of (F) -- 1/9(3F)+ 1/25(5F)- 1/49(7F)+ . . . FIG. 6h
illustrates schematically a plot in frequency space (i.e. frequency
f against amplitude A) of the frequency components of the waveform
in FIG. 6g. Again, the amplitude A has been normalized so as to be
1 for the largest amplitude A of the spectrum. The plot of FIG. 6h
illustrates that, the triangular waveform comprises the fundamental
frequency component having frequency F, as well as further
frequency components at odd integer multiples (odd harmonics) of
the fundamental frequency F, i.e. 3F, 5F, etc., having relative
amplitudes represented as 1(F); 1/9(3F); 1/25(5F) etc. In other
words, as illustrated, some of the amplitude or energy of the
waveform of FIG. 6g is contained at the frequency F, i.e. the
fundamental frequency component of the waveform; a ninth as much
energy as in the fundamental frequency component is contained in
the further frequency component at frequency 3F, and a 25th as much
energy as in the fundamental frequency component is contained in
the further frequency component at frequency 5F (and so on).
[0080] FIG. 6i illustrates schematically another example plot of a
waveform of alternating current I as a function of time t. In this
example, the waveform is a sawtooth waveform. In this example, the
sawtooth waveform has a fundamental frequency F. As is known, the
Fourier expansion of a sawtooth wave comprises a sum (in the ideal
an infinite sum, but in practice not infinite) of sine waves,
conforming to a sequence (in the form of the above introduced
convention) of (F)-1/2(2F)+1/3(3F)-1/4(4F)+ . . . FIG. 6j
illustrates schematically a plot in frequency space (i.e. frequency
f against amplitude A) of the frequency components of the waveform
in FIG. 6i. Again, the amplitude A has been normalized so as to be
1 for the largest amplitude A of the spectrum. The plot of FIG. 6j
illustrates that, the sawtooth waveform comprises the fundamental
frequency component having frequency F, as well as further
frequency components at integer multiples (harmonics) of the
fundamental frequency F, i.e. 2F, 3F, etc., having relative
amplitudes represented as 1(F); 1/2(2F); 1/3(3F) etc. In other
words, as illustrated, some of the amplitude or energy of the
waveform of FIG. 6i is contained at the frequency F, i.e. the
fundamental frequency component of the waveform; half as much
energy as in the fundamental frequency component is contained in
the further frequency component at frequency 2F, and a third as
much energy as in the fundamental frequency component is contained
in the further frequency component at frequency 3F (and so on).
[0081] Hence, in each of FIGS. 6c, 6e, 6g, and 6i, (e.g. square,
triangular, sawtooth), the alternating current has a waveform
comprising a fundamental frequency component having a first
frequency (e.g. F) and one or more further frequency components
each having a frequency higher than the first frequency. For
example, the first frequency may be a frequency F in the range 0.5
MHz to 2.5 MHz, and the frequency of each of the one or more
further frequency components may be nF, where n is a positive
integer greater than 1. For example, in the case of the square
waveform (or otherwise), n may be an odd positive integer greater
than 1. For example, the first frequency F may be 2 MHz, and the
frequency of the first further frequency component in the case of a
square waveform (or otherwise) may be 3*2 MHz, i.e. 6 MHz. It will
be appreciated that there are many example waveforms, other than
the examples shown in FIGS. 6c, 6e, 6g, and 6i, which comprise a
fundamental frequency component having a first frequency (e.g. F)
and one or more further frequency components each having a
frequency higher than the first frequency, which may be used
instead. Nonetheless, it is noted that, among possible waveforms
conforming to this criterion, the square waveform has a high
proportion (around 20%) of its energy in higher order frequency
components, and may therefore provide particular benefits in
reducing the skin depth of the induced alternating current in the
susceptor portion of the susceptor, as described in more detail
below.
[0082] As mentioned above, the skin depth may be defined as a
characteristic depth into which the alternating magnetic field
produced by the induction element 108 penetrates into the susceptor
portion to cause inductive heating. Specifically, the skin depth
may be defined as the depth below the surface of the susceptor
where the induced current density falls to 1/e (i.e. about 0.37) of
its value at the surface of the susceptor. The skin depth is
dependent on the frequency f of the induced current, and hence in
turn dependant on the frequency of the alternating magnetic field
produced by the induction element, and hence in turn dependant on
the frequency of the alternating current driven through the
induction element. For example, the frequency of the induced
current may be the same as the frequency of the alternating current
driven through the induction element. Specifically, skin depth
.delta. may be given by:
.delta. = 2 .times. .rho. 2 .times. .pi. .times. .times. f .times.
.times. .mu. ( 1 ) ##EQU00001##
[0083] where .rho. is the resistivity of the susceptor, f is the
frequency of the induced current (which may be the same as the
frequency of the alternating current driven through the induction
element), and .mu.=.mu.r.mu..sub.0 where .mu.r is the relative
magnetic permeability of the susceptor and .mu..sub.0 is the
permeability of free space.
[0084] Driving the induction element with a current having a
waveform comprising a fundamental frequency component having a
first frequency and one or more further frequency components having
a frequency higher than the first frequency, in turn causes the
alternating magnetic field produced by the induction element to
comprise a fundamental frequency component having the first
frequency and the one or more further frequency components of
having a frequency higher than the first frequency, which in causes
the induced alternating current in the susceptor to comprise a
fundamental frequency component having the first frequency and the
one or more further frequency components of having a frequency
higher than the first frequency. The further frequency components
of the induced current are associated with a smaller skin depth
than the fundamental frequency components of the induced
current.
[0085] Therefore, driving the induction element with an alternating
current having a waveform comprising the fundamental frequency
component and the one or more higher frequency components may
therefore allow a greater proportion of the inductive energy
transfer from the induction element to the susceptor to occur at
relatively small distances from the surface of the induction
element, for example as compared to using the fundamental frequency
alone. This may allow advantages.
[0086] For example, having a greater proportion of the inductive
energy transfer from the induction element to the susceptor occur
at relatively small distances from the surface of the induction
element may allow the thickness of susceptor portion 224, 324 to be
reduced while still substantially maintaining a given inductive
energy transfer efficiency. For example, an alternating current
having a pure sine waveform of frequency F may have 100% of the
inductive energy transfer occurring at frequency F, and hence may
have a skin depth within which a given proportion of the inductive
energy transfer takes place. However, for a square waveform
alternating current having the same fundamental frequency F, around
20% of the inductive energy transfer is provided by the further
frequency components of higher frequency (and hence lower
associated skin depths), and hence the skin depth within which the
given proportion of inductive energy transfer takes place will be
reduced. Accordingly, the susceptor portion 224, 324 may be made
thinner (as compared to for the case where the pure sine waveform
is used), without reducing the given absorption efficiency.
Accordingly, less material (for example ferromagnetic material, for
example nickel or cobalt) may be used for the susceptor portion,
which may in turn allow the cost of the susceptor portion to be
reduced and/or the efficiency of producing the susceptor portion
224, 324 to be increased.
[0087] As another example, having a greater proportion of the
inductive energy transfer from the induction element to the
susceptor occur at relatively small distances from the surface of
the induction element may allow the inductive energy transfer
efficiency to be increased for a given susceptor portion thickness
(for example one in which the skin depth might otherwise be larger
than the thickness of the susceptor portion). For example, a given
susceptor portion 224, 324 may have a given thickness. When a pure
sine waveform alternating current of frequency F is used, the skin
depth may be larger than the thickness of the susceptor portion
224, 324, and hence a relatively low inductive energy transfer may
be achieved. However, for a square waveform alternating current
having the same fundamental frequency F, around 20% of the
inductive energy transfer is provided by the further frequency
components of higher frequency (and hence lower associated skin
depths), and hence there may be a relatively higher inductive
energy transfer to the susceptor portion having the given
thickness, and hence the efficiency of the inductive energy
transfer to the susceptor portion 224, 324 may be relatively
increased.
[0088] Referring to FIG. 7, there is illustrated an example method
of operating an aerosol generating apparatus. For example, the
aerosol generating apparatus may be the aerosol generating
apparatus 100 described above with reference to any one of FIGS. 1
to 5. For example, the aerosol generating apparatus 100 may
comprise a composite susceptor 110, 210, 310 arranged for heating
an aerosol generating material 116 thereby to generate an aerosol.
As described above, the composite susceptor may comprise a heat
resistant support portion 222, 322 and a susceptor portion 224, 324
supported by the support portion 222, 322. For example, as
described above, the support portion 222, 322 may be or comprise
one or more of a metal such as stainless steel, aluminum, steel,
copper; a metal alloy, a ceramics material, and a plastics
material, and/or a high temperature (i.e. heat resistant) polymer
such as Polyether ether ketone (PEEK) and/or Kapton. In some
examples, the support portion may comprise paper. For example, as
described above, the susceptor portion 224, 324 may be or comprise
a ferromagnetic material, for example nickel or cobalt, for example
formed as a coating on the support structure, for example having a
thickness of less than 50 microns, for example less than 20
microns, for example between 10 and 20 microns, or for example a
few microns. The apparatus may further comprise an induction
element 108 arranged for inductive energy transfer to at least the
susceptor portion 224, 324 of the composite susceptor 210.
[0089] The method comprises, in step 700, driving the induction
element 108 with an alternating current thereby to cause the
inductive energy transfer to the susceptor portion 224, 324,
thereby to cause the heating of the aerosol generating material 116
by the composite susceptor 110, 210, 310, thereby to generate the
aerosol; wherein the alternating current has a waveform comprising
a fundamental frequency component having a first frequency (F) and
one or more further frequency components each having a frequency
higher than the first frequency (F). For example, as described
above, the one or more further frequency components may be
harmonics of the fundamental frequency component (i.e. having
frequencies of integer multiples of the fundamental frequency), for
example odd harmonics (i.e. having frequencies of odd integer
multiples of the fundamental frequency. For example, as described
above, the waveform may be one of a triangular waveform, a sawtooth
waveform, and a square waveform. For example, as described above,
the waveform may be a bi-polar square waveform. The driving the
induction element with the alternating current may be performed by
a driver arrangement, for example, the driver arrangement 106
described above with reference to any one of FIGS. 1 to 6, which
may for example comprise transistors in a H-bridge arrangement
controlled so as to produce a driving current having a square
waveform, as described above.
[0090] In a similar way to as described above, the method may
provide for the cost of the susceptor portion 224, 324 to be
reduced while still substantially maintaining a given inductive
energy transfer efficiency (and hence aerosol generation
efficiency), and/or allow for an improved inductive energy transfer
efficiency (and hence aerosol generation efficiency) for a given
susceptor portion 224, 324 thickness.
[0091] According to the above examples therefore, an improved
aerosol generating device and method for producing an aerosol may
be provided.
[0092] In the above described examples, an induction element 108 is
driven with alternating current having a waveform (e.g. a square
waveform) comprising a fundamental frequency component and one or
more higher frequency components (e.g. harmonics), to cause
inductive energy transfer to a susceptor portion 223, 324 of a
composite susceptor 110, 210, 310, the composite susceptor 110,
210, 310 comprising the susceptor portion 224, 324 and a support
portion supporting the susceptor portion 224, 324. Some benefits of
this arrangement are discussed above. However, the following is
also noted:
[0093] Since the support portion 222 supports the susceptor portion
224, 324, the susceptor portion 224 may be made thin (e.g. 50
microns, for example no more than 20 microns, for example between
around 10 to 20 microns, for example around 15 microns or for
example a few microns) because the susceptor portion 224, 324 need
not support itself. Having a thin susceptor portion 224, 324 may
allow numerous benefits. For example, the mass of the susceptor
portion 224, 324 may be relatively small and hence the susceptor
portion 224, 324 may heat up relatively quickly for a given
inductive energy transfer, and hence in turn the heat up rate of
the aerosol generating material may be increased, which may provide
for more responsive heating performance and/or for improved overall
energy efficiency. As another example, the amount of susceptor
portion 224 material may be relatively small, thereby saving costs
of the susceptor material. As another example, the thickness of the
susceptor portion 224, 324 may be relatively small, which may allow
the time and costs associated with manufacturing the susceptor
portion 224, 324, for example by deposition, chemical and/or
electrochemical plating, and/or vacuum evaporation, to be reduced.
As another example, for manufacturing of the susceptor portion by
deposition or evaporation for example, the morphology of the
deposited susceptor portion layer may worsen with increasing
thickness of the layer, and hence having a thin susceptor portion
224, 324 may allow for the overall quality of the layer to be
relatively high, which may allow for example for improved
performance.
[0094] Therefore, the composite susceptor 110, 210, 310 allows for
use of relatively thin susceptor portions 224, 324, which may have
benefits as above. However, relatively thin susceptor portions 224,
324 could in principle have the drawback that the efficiency of
inductive energy transfer from the induction element 108 to the
relatively thin susceptor portion 224, 324 may be relatively small.
For example, as described above, this may be because the skin depth
(the characteristic depth into which the alternating magnetic field
produced by the induction element 108 penetrates the susceptor
portion to cause inductive heating) may be larger than the
thickness of the susceptor portion 224, 324, meaning that the
coupling efficiency of the inductive energy transfer from the
induction element 108 to the susceptor portion 224, 324 may be
relatively low. However, this potential drawback of composite
susceptors 110, 210, 310 may be addressed, as per the examples
described herein, by driving the induction element 108 with
alternating current having a waveform comprising a fundamental
frequency component and one or more higher frequency components
(e.g. harmonics). Since the skin depth decreases with increasing
frequency, the higher frequency components may help ensure that,
for the relatively thin susceptor portion 224, 324 of the composite
susceptor 110, 210, 310, a relatively high coupling efficiency of
the inductive energy transfer from the induction element 108 to the
susceptor portion 224, 324 may nonetheless be achieved. This may be
achieved for example without increasing the fundamental frequency
of the driving alternating current. As described above, of such
waveforms, the square waveform, such as the bi-polar square wave
form, has a particularly high proportion of its energy in higher
frequency components, and hence may allow for particularly high
coupling efficiency to the susceptor portion 224, 324 of the
composite susceptor 110, 210, 310. Moreover, as described, the
square waveform, for example bi-polar square waveform, may be
generated using a relatively inexpensive and uncomplicated driver
arrangement 432.
[0095] Therefore, the combination of the composite susceptor 110,
210, 310 and the driving of the induction element with an
alternating current having a waveform (e.g. a square waveform)
comprising a fundamental frequency component and one or more higher
frequency components, may allow for reduction of costs for example
while helping to ensure a relatively high energy transfer
efficiency, and hence may allow for an improved aerosol generating
device and method.
[0096] Though in certain examples described above the susceptor
portion of the composite susceptor comprises a coating on the
support portion, in other examples the susceptor portion and the
support portion may each comprise a sheet of material. The support
portion may be separable from the susceptor portion. The support
portion may then abut the susceptor portion to support the
susceptor portion, e.g. the support portion may surround the
susceptor portion. For example, the susceptor portion may comprise
a first sheet of a material configured to be wrapped around the
aerosol generating material while the support portion comprises a
second sheet of material configured to be wrapped around the first
sheet to support the first sheet. In one such example, the support
portion is formed of paper. The susceptor portion may be formed of
any suitable material for generating heat due to the alternating
magnetic field. For example, the susceptor portion may comprise
aluminum.
[0097] The above examples are to be understood as illustrative
examples of the invention. It is to be understood that any feature
described in relation to any one example may be used alone, or in
combination with other features described, and may also be used in
combination with one or more features of any other of the examples,
or any combination of any other of the other examples. Furthermore,
equivalents and modifications not described above may also be
employed without departing from the scope of the invention, which
is defined in the accompanying claims.
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